Vehicle electrical systems in motor vehicles have a multitude of electrical consumers that are supplied with electrical energy from an energy supply, e.g., as a battery or a generator. In addition, vehicle electrical systems also have electromechanical or electronic components such as switches and voltage converters.
The electrical energy in the motor vehicle should be available such that the motor vehicle is able to be started at any time and a sufficient current supply is ensured during the operation so that, as a minimum, safety-related devices such as the brakes, the steering system and also the lights are supplied in a reliable and uninterrupted manner. In the off state, electrical consumers should still be operable for an adequate period of time without making a subsequent start impossible. It should be noted that an interruption in the supply of the consumers may occur in case of a malfunction in the voltage supply or a short-circuit in the vehicle electrical system, which in turn results in a failure of functionalities of the motor vehicle.
The introduction of novel electronic and mechatronic systems in the motor vehicle, such as electrical steering systems or novel assistance systems, e.g., the brake assistant or an adaptive cruise control, which lower the energy consumption of the vehicle and markedly enhance the safety and comfort for the driver, is currently on the rise. In the future, further systems that allow for autonomous or partially autonomous driving are in the planning stage or are currently being developed. If such systems are installed in a vehicle, they, too, must operate reliably and meet the demands of functional safety. Specifically to be avoided in this context are what are termed common cause errors or single errors, which then lead to an abrupt malfunction of the entire system or subsystem.
Thus, the use of such new systems also places higher demands on the safety and availability of the vehicle electrical system inasmuch as these systems are, for the most part, supplied from the standard 12V vehicle electrical system of the vehicle. Vehicle electrical systems with a higher voltage are also used, especially for commercial vehicles. Under no circumstances should a failure of the vehicle electrical system on the basis of a single error lead to a failure of a safety-related system that is indispensable for the safe functioning of the vehicle and which draws its energy from the 12V vehicle electrical system.
A single fault, such as a short circuit in the vehicle electrical system or the failure of a battery or the generator, should not lead to the loss of the steering or braking ability of the vehicle. A defect of this type may also not lead to the abrupt failure of a system for the autonomous or partially autonomous control of the vehicle, for example. A driver of an automobile who relies on the system and possibly just happens to be inattentive might then perhaps react too late or incorrectly in the event of a sudden failure, which could lead to a dangerous situation.
The currently most frequently installed vehicle electrical system with a generator and a 12V battery is largely sufficient for the presently installed electrical systems. Novel safety-related systems, whose function is indispensable for the safe operation of the vehicle, require novel vehicle-electrical system topologies, which ensure the energy supply for these safety-related consumers in a reliable manner.
As already mentioned, safety-relevant consumers that carry out important functions in the motor vehicle and must not fail under any circumstances are provided in modern vehicle electrical systems to an increasing extent. In order to ensure this, it is known to connect safety-related consumers to one or multiple vehicle electrical subsystems, each vehicle electrical subsystem having its own energy supply that may include a battery and/or a generator, for instance. In the event of a failure of the energy supply of a vehicle electrical subsystem, safety-related consumers are able to be supplied from other vehicle electrical subsystems and can thereby maintain their operation.
The printed publication DE 10 2005 004 330 A1 describes a vehicle electrical system for safety-related consumers, which includes at least two vehicle electrical subsystems, in which a safety-related consumer is to be supplied with a supply voltage via two different supply paths, the supply paths being able to be decoupled from each other with the aid of decoupling means. In addition, the safety-related consumer is able to be connected to at least two energy accumulators by way of at least four supply paths.
Known from the printed publication DE 102 51 589 A1 is a vehicle electrical system having at least two vehicle electrical subsystems in which a respective supply voltage is available. Provided in the vehicle electrical system is a safety-related consumer, which is connected to one of the vehicle electrical subsystems. A supply voltage is able to be applied to this consumer via two different supply paths, and the supply paths are able to be decoupled from each other with the aid of decoupling means, such a switches.